The highly contagious norovirus, known for causing an uncomfortable, day-long stomach illness, is on the rise in Canada following a pandemic lull, federal health officials confirmed to CBC News.
Since early January, reported cases of norovirus “have increased both nationally and in several provinces,” including British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, New Brunswick and Newfoundland and Labrador, the Public Health Agency of Canada (PHAC) , said in an email response to questions about spikes in cases in the US and UK
Infections identified by PHAC’s surveillance program since early 2023 are “generally comparable” to those reported during the same period in recent seasons before the pandemic, spokeswoman Anna Maddison said. PHAC did not provide hard data as the numbers reported by the provinces are “preliminary”.
Faced with uncomfortable and in some cases deadly symptoms – including stomach pain, vomiting, diarrhea, weakness and dehydration – the virus’ surge in Canada provides another crude reminder of just how many pathogens are back in circulation this winter.
“What we’re seeing is the number of infections returning to normal pre-pandemic baseline levels,” said Lawrence Goodridge, a professor of microbiology at the University of Guelph and an expert in food safety and norovirus surveillance.
In recent years, COVID-19 restrictions and infection-prevention measures like washing hands and wearing masks likely helped keep norovirus at bay while people circulated less than usual, he said.
“But as things have eased and things have opened up and things are getting back to normal, we are starting to see [more cases].”
Cases in the US, UK
South of the border, the U.S. Centers for Disease Control and Prevention (CDC) also recently reported a spike in cases, nearly reaching pre-pandemic levels.
From August through early January, 225 norovirus outbreaks were reported by states participating in a federal surveillance program, CDC data shows. That compares to 172 norovirus outbreaks reported by the same states during the same period last season.
And in the UK, norovirus is also back with a vengeance, with national surveillance data showing laboratory reports of the virus are 66 per cent higher than the average for this time of year.
Care homes are seeing a surge in outbreaks, and the biggest rise in cases is in people aged 65 and over, Britain’s Health Security Agency said in a press release.
“While a high number of cases in this age group is expected at this time of year,” the agency continued, “these levels have not been observed in over a decade.”
Typically spread through contaminated food such as raw shellfish or imported fruit, norovirus is also highly transmissible in closed settings including homes, nursing homes, cruise ships and daycares.
In 2022, BC oysters have been linked to hundreds of cases in several provinces and parts of the US, mostly in people who ate contaminated raw oysters between January and March of that year.
“It can really spread like wildfire just because it’s a very, very contagious virus — you don’t have to be exposed to a lot of it at all to get an infection,” said virologist Angela Rasmussen of the University of Saskatchewan’s Vaccine and Organization for infectious diseases.
“And unfortunately, when you’re infected with the norovirus, most of the time you’ve got pretty severe gastroenteritis, and that leads to hair loss [the virus] … hopefully into the bathroom around you. But if people don’t wash their hands, other surfaces can become contaminated.”
The onset of the disease is typically quite sudden, said Christiane Wobus, associate professor of microbiology and immunology at the University of Michigan.
“If you’ve had contact with someone who was sick,” she said, “you can show symptoms within 12 hours.”
Washing hands, cleaning surfaces can curb transmission
Long known as “winter vomiting disease,” norovirus spreads in the northern hemisphere primarily between November and April, when people spend more time indoors.
Unlike some other viruses, such as SARS-CoV-2, the causative agent of COVID-19, norovirus is particularly robust on surfaces, Goodridge said.
The most important ways to reduce transmission include washing hands, cleaning common surfaces, isolating as much as possible from others at home, and keeping family members away from school and work if they have symptoms.
The family doctor Dr. Allan Grill, chief of family medicine at Markham Stouffville Hospital in Markham, Ontario, said it’s also important to keep an eye on vulnerable loved ones, including frail seniors and — particularly — children who may be at a higher risk of becoming dehydrated become.
“Don’t you feed them too? They do [fewer] wet diapers for 24 hours?” he said.
In these cases, it’s important to keep children hydrated by giving them plenty of fluids and taking them to first aid or the emergency room if their symptoms don’t improve within a few days.
Because many people with upset stomachs never set foot in a doctor’s office — and those who do may not necessarily get tested — Grill said the number of cases in any given year is likely too low. (Federal figures suggest norovirus sickens more than a million Canadians each year.)
To spot norovirus outbreaks more quickly, Goodridge and other researchers are trying to use wastewater monitoring to improve surveillance efforts — work he said has “derailed” in the pandemic when all eyes turned to COVID-19 straightened, but are now back on course.
“We are increasingly looking for other foodborne pathogens now that the pandemic is ending,” he said.
